ah ok. i dont have this behavior.
It happened to me in alpha 18 also.
This used to always happen to me, but with the latest builds, I don't see this error except for very rarely.
Edited on 4/20/17 to add: And I just saw this yesterday again.
still seeing this with release 707 of a 21
but only the ones that were against a wall or cliff
Still present as of A22 r729. Triggers not only near cliffs/water but also near harvestable stones and/or resource nodes (tumbleweeds, pear cacti etc).
I have had this show up for the building part and it showed a spot not being put in.... it was filled when you allow them to build a little part of it, tell them to stop and allow them to build it again.... fixed (or it might be just me)